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HomeMy WebLinkAboutENGINEERING LETTER - 17-00745 - 621 Eaglewood Dr - Solar PanelTo: Blue Raven Solar 1220 S. 630 E Ste. 430 American Fork, UT 84003 Subject: Certification Letter Johnson Residence 621 Eaglewood Drive Rexburg, ID. 83440 To Whom It May Concern, The spacing of the solar standoffs should be kept at 48" o.c. with a staggered pattern to ensure proper distribution of loads. November 27, 2017 A jobsite observation of the condition of the existing framing system was performed by an audit team from Blue Raven  Solar. All attached structural calculations are based on these observations and the design criteria listed below. On the above referenced project, the roof structural framing has been reviewed for additional loading due to the  installation of the solar PV addition to the roof. The structural review, including the plans and calculations only apply to the  section of the roof that is directly supporting the solar PV system and its supporting elements. The observed roof framing is  described as follows. The roof structure of (MP1) consists of composition shingle on roof plywood that is supported by pre‐manufactured trusses  that are spaced at @ 24"o.c.. The top chords, sloped at 27 degrees, are 2x4 sections, the bottom chords are 2x4 sections  and the web members are 2x4 sections. The truss members are connected by steel gusset plates. The max unsupported  projected horizontal top chord span is approximately 6'‐0''.  The roof structure of (MP2&3) consists of composition shingle on roof plywood that is supported by pre‐manufactured  trusses that are spaced at @ 24"o.c.. The top chords, sloped at 27 degrees, are 2x4 sections, the bottom chords are 2x4  sections and the web members are 2x4 sections. The truss members are connected by steel gusset plates. The max  unsupported projected horizontal top chord span is approximately 6'‐3''.  The existing roof framing system of (MP1) is judged to be adequate to withstand the loading imposed by the installation of  the solar panels. No reinforcement is necessary. Where required for standoff attcahments, install a vertical2x4 block  between adjecent trusses. Attach block to trusses per detail. The existing roof framing system of (MP2&3) is judged to be adequate to withstand the loading imposed by the installation  of the solar panels. No reinforcement is necessary.  Johnson Residence, Rexburg, ID 1 Design Criteria: ● Applicable Codes = 2009 IBC/IRC, ASCE 7‐05 ● Roof Dead Load = 7 psf (MP1)  ‐‐  7 psf (MP2&3) ● Roof Live Load = 20 psf ● Wind Speed = 90 mph, Exposure C ● Sincerely, Paul Zacher, P.E. Project Engineer Ground Snow Load = 50 psf  ‐  Roof Snow Load = 35 psf Please contact me with any further questions or concerns regarding this project. Johnson Residence, Rexburg, ID 2 R E E NI REHCAZK.LUAP GNELANOISSEFORP 2762 FOETAT S OHADI DESNECIL EXP. 08/31/2018 Gravity Loading 50 psf (ASCE7 - Eq 7-1) 1 (ASCE7 - Table 7-2) 1 (ASCE7 - Table 7-3) 1 35.0 psf (ASCE7 - Eq 7-2) 1 35.0 psf 3.0 psf 4.00 ft 2.67 ft 10.68 sft 32 lb 4.00 2.00 0.73 0.00 (Ceiling Not Vaulted) 0.27 7.0 psf 7.9 psf 4.00 2.00 0.73 0.00 (Ceiling Not Vaulted) 0.27 7.0 psf 7.86 PV Dead Load = 3 psf (Per Blue Raven Solar) DL Adjusted to 27 Degree Slope Point Loads of Standoffs DL Adjusted to 27 Degree Slope Miscellaneous Vaulted Ceiling Roof Live Load = 20 psf Roof Plywood Roof Dead Load (MP1) Composition Shingle Note: Roof live load is removed in area's covered by PV array. Roof Snow Load Calculations pg = Ground Snow Load = Ce = Exposure Factor = pf = 0.7 Ce Ct I pg Ct = Thermal Factor = I = Importance Factor = Cs = Slope Factor = Standoff Tributary Area = ps = Cspf ps = Sloped Roof Snow Load = pf = Flat Roof Snow Load = PV System Weight Weight of PV System (Per Blue Raven Solar) X Standoff Spacing = Y Standoff Spacing = Note: PV standoffs are staggered to ensure proper distribution of loading Roof Plywood Vaulted Ceiling 2x4 Top Chords @ 24"o.c. 2x4 Top Chords @ 24"o.c. Miscellaneous Total Roof DL (MP2&3) Total Roof DL (MP1) Roof Dead Load (MP2&3) Composition Shingle Johnson Residence, Rexburg, ID 3 Wind Calculations 90 mph C Gable/Hip 27 degrees 20 ft 17.4 ft (Eq_6-15) 0.9 (Table 6-3) 1 (Fig. 6-4) 0.85 (Table 6-4) 90 mph 1 (Table 6-1) qh = 15.86 Zone 1 Zone 2 Zone 3 Positive GCp = -0.85 -1.45 -2.30 0.40 (Fig. 6-11) Uplift Pressure = -13.47 psf -22.95 psf -36.42 psf 10.0 psf (Minimum) X Standoff Spacing = 4.00 4.00 2.67 Y Standoff Spacing = 2.67 2.67 2.67 Tributary Area = 10.68 10.68 7.12 Footing Uplift = -144 lb -245 lb -259 lb -259 lb 400 lb Therefore, OK Fastener =1 - 5/16" dia Lag Number of Fasteners = 1 Embedment Depth = 2.25 Pullout Capacity Per Inch = 250 lb Fastener Capacity = 563 lb w/ F.S. of 1.5 = 376 lb Therefore, OK Input Variables Wind Speed Effective Wind Area Design Wind Pressure Calculations Roof Shape Standoff Uplift Calculations Roof Slope 376 lb capacity > 259 lb demand Maximum Design Uplift = Standoff Uplift Capacity = 400 lb capacity > 259 lb demand Fastener Capacity Check Standoff Uplift Check Kz (Exposure Coefficient) = Kzt (topographic factor) = Kd (Wind Directionality Factor) = V (Design Wind Speed) = Importance Factor = qh = 0.00256 * Kz * Kzt * Kd * V^2 * I Wind Pressure P = qh*G*Cn Exposure Category Per ASCE 7-05 Components and Cladding Mean Roof Height Johnson Residence, Rexburg, ID 4 Framing Check (MP1)PASS Dead Load 7.9 psf PV Load 3.0 psf Snow Load 35.0 psf Governing Load Combo = DL + SL Total Load 45.9 psf Fb (psi) = f'b x Cd x Cf x Cr (NDS Table 4.3.1) 900 x 1.15 x 1.5 x 1.15 Allowed Bending Stress = 1785.3 psi (wL^2) / 8 = 412.707 ft# = 4952.48 in# Actual Bending Stress = (Maximum Moment) / S = 1617.2 psi L/180 (E = 1600000 psi Per NDS) = 0.4 in Deflection Criteria Based on = (w*L^4) / (185*E*I) = = L/554 > L/180 Therefore OK Allowed Deflection (Live Load) =L/240 0.3 in (w*L^4) / (185*E*I) L/728 > L/240 Therefore OK Member Area = Fv (psi) = 180 psi (NDS Table 4A) Allowed Shear = Fv * A = Max Shear (V) = w * L / 2 = 275 lb Check Bending Stress Continuous Span 0.130 in 0.099 in Member Properties Member Size 2x4 S (in^3) 3.06 DF#2 Member Spacing @ 24"o.c. Maximum Moment = Check Deflection I (in^4) 5.36 Lumber Sp/Gr Actual Deflection (Live Load) = Allowed Deflection (Total Load) = Actual Deflection (Total Load) = Allowed > Actual -- 90.6% Stressed -- Therefore, OK 945 lb Allowed > Actual -- 29.2% Stressed -- Therefore, OK (True Dimensions) 5.3 in^2 Check Shear w = 92 plf 2x4 Top Chords @ 24"o.c. Member Span = 6' - 0" Johnson Residence, Rexburg, ID 5 Framing Check (MP2&3)PASS Dead Load 7.9 psf PV Load 3.0 psf Snow Load 35.0 psf Governing Load Combo = DL + SL Total Load 45.9 psf Fb (psi) = f'b x Cd x Cf x Cr (NDS Table 4.3.1) 900 x 1.15 x 1.5 x 1.15 Allowed Bending Stress = 1785.3 psi (wL^2) / 8 = 447.815 ft# = 5373.78 in# Actual Bending Stress = (Maximum Moment) / S = 1754.8 psi L/180 (E = 1600000 psi Per NDS) = 0.416 in Deflection Criteria Based on = (5*w*L^4) / (384*E*I) = = L/204 > L/180 Therefore OK Allowed Deflection (Live Load) =L/240 0.312 in (5*w*L^4) / (384*E*I) L/267 > L/240 Therefore OK Member Area = Fv (psi) = 180 psi (NDS Table 4A) Allowed Shear = Fv * A = Max Shear (V) = w * L / 2 = 287 lb Simple Span 0.281 in 0.368 in 945 lb Allowed > Actual -- 30.4% Stressed -- Therefore, OK Check Bending Stress Maximum Moment = Allowed > Actual - 98.3% Stressed -- Therefore, OK Check Deflection Allowed Deflection (Total Load) = Actual Deflection (Total Load) = Actual Deflection (Live Load) = (True Dimensions) w = 92 plf 2x4 Top Chords @ 24"o.c. Member Span = 6' - 3" Member Properties Member Size S (in^3) I (in^4) Lumber Sp/Gr Member Spacing 2x4 3.06 5.36 DF#2 @ 24"o.c. Check Shear 5.3 in^2 Johnson Residence, Rexburg, ID 6 Lateral Check Level Area Weight (psf) Weight (lb) Roof 3000 sf 7.9 psf 23569 lb Ceiling 3000 sf 6.0 psf 18000 lb 7/8" Stucco 100 ft 11.0 psf 4400 lb (8'-0" Wall Height) Int. Walls 100 ft 6.4 psf 2560 lb 48529 lb 3.0 psf 348 sf 1044 lb 4853 lb 1044 lb 2.2% 4853 lb > 1044 lb, Therefore OK Per 2009 IBC Chapter 34 Existing Weight of Effected Building Existing Weight of Effected Building Proposed Weight of PV System Weight of PV System (Per Blue Raven Solar) Approx. Area of Proposed PV System Approximate Total Weight of PV System 10% Comparison 10% of Existing Building Weight (Allowed) Approximate Weight of PV System (Actual) Percent Increase Johnson Residence, Rexburg, ID 7